JP2010021232A - Semiconductor device and manufacturing method thereof - Google Patents

Abstract

To provide a semiconductor device which is normally off by optimizing the film thickness and Al composition ratio of an electron supply layer.
In a semiconductor device, an electron transit layer is formed on a substrate by epitaxial growth, and an electron supply layer is further formed on the electron transit layer by epitaxial growth. The electron transit layer 17 and the electron supply layer 15 have a heterojunction structure, and a HEMT capable of forming a two-dimensional electron gas channel 16 at the junction interface. The electron supply layer 15 is covered with an insulating film 14, and a source electrode 11, a gate electrode 12, and a drain electrode 13 are provided. The electron supply layer 15 is formed with an Al composition ratio of 10 to 18 [%] and a film thickness of 5 to 15 [nm]. The manufactured semiconductor device 10 is normally off because the occurrence of cracks and the like is prevented. Therefore, this semiconductor device 10 can be used as a power device.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor device having a heterojunction structure of an electron supply layer and an electron transit layer, and a method for manufacturing the same.

In the conventional semiconductor device, the composition ratio of Al (aluminum) in the AlGaN (aluminum gallium nitride) layer (hereinafter simply referred to as “Al composition ratio”) is x%, the film thickness of the AlGaN layer is y nm, and x High electron mobility transistor (HEMT) in which y satisfies the formula [x + y <55, 25 ≦ x ≦ 40, y ≧ 10] and forms a two-dimensional electron gas at the junction interface between the AlGaN layer and the GaN (gallium nitride) layer An example of a technique called “mobility transistor” is disclosed (see, for example, Patent Document 1). According to this semiconductor device, since the film thickness of the AlGaN layer is made thinner than the critical film thickness to prevent the occurrence of cracks, the change in sheet resistance with time can be eliminated.
JP 2007-324363 A

  However, in the semiconductor device of Patent Document 1, the transistor is normally turned on under the influence of the high concentration two-dimensional electron gas generated at the hetero boundary surface, and the transistor is not turned off unless the gate voltage is made negative. When an inverter circuit is configured using this semiconductor device, for example, when the control signal of the gate voltage disappears (that is, becomes 0) during the operation of the inverter, two transistors connected in series are simultaneously turned on to supply power. There is a problem that a short circuit occurs and the inverter circuit is damaged. Therefore, in order to use the semiconductor device as a power device, it is necessary to make the semiconductor device normally off.

On the other hand, in a HEMT having a heterojunction structure of an AlGaN layer and a GaN layer, the gate threshold voltage is negative, but the gate threshold voltage linearly changes in the positive direction as the AlGaN layer thickness is reduced. It has been known. Therefore, in order to manufacture a normally-off semiconductor device, it is desirable to make the AlGaN layer as thin as possible. However, there is a problem that cracks and the like are more likely to occur as the film thickness decreases.
It is also known that when the Al composition ratio of the AlGaN layer is changed, the sensitivity of the gate threshold voltage to the Al composition ratio increases as the thickness of the AlGaN layer increases. Therefore, in order to manufacture a normally-off semiconductor device, it is desirable to make the Al composition ratio as low as possible. However, there is a problem that the film thickness of the AlGaN layer must be reduced as the Al composition ratio of the AlGaN layer decreases.
For this reason, in order to appropriately manufacture a normally-off semiconductor device, it is necessary to optimize the film thickness and the Al composition ratio of the AlGaN layer.

  The present invention has been made in view of such a point, and optimizes the film thickness and the Al composition ratio of an electron supply layer (for example, the above-described AlGaN layer), and a semiconductor device that is normally off and its manufacture It aims to provide a method.

(1) Means for solving the problem (hereinafter simply referred to as “solution means”) 1 is formed on a substrate and is formed of a nitride III-V compound containing at least aluminum as a group III element. The electron supply layer and the electron transit layer formed of the nitride-based III-V group compound have a heterojunction structure, and the electron supply layer has an aluminum composition ratio (Al composition ratio). The gist is that the film thickness is 10 to 18% and the film thickness is 5 to 15 nm.

The “electron supply layer” may be formed of a nitride III-V group compound containing at least aluminum as a group III element. That is, the group III element includes at least one of the group consisting of Ga (gallium), Al (aluminum), B (boron), and In (indium), and Al is an essential element. The group V element includes at least one of the group consisting of N (nitrogen), P (phosphorus), and As (arsenic).
The “electron transit layer” only needs to be formed of a nitride-based III-V group compound. That is, it is the same as the electron supply layer except that Al is a selective element.

  According to Solution 1, when the Al composition ratio is 10 to 18% and the film thickness is 5 to 15 nm, the occurrence of cracks and the like is prevented, and the manufactured semiconductor device is normally off. Therefore, this semiconductor device can be used as a power device.

(2) Solution 2 is the semiconductor device described in Solution 1, which is a HEMT or MESFET (Metal-Semiconductor Field Effect Transistor) that forms a two-dimensional electron gas at the junction interface between the electron supply layer and the electron transit layer. The main point is that it is a metal-semiconductor field effect transistor.

  According to Solution 2, a HEMT or MESFET can be provided as a normally-off semiconductor device.

(3) Solution 3 is formed of a nitride-based III-V group compound formed of a nitride-based III-V compound containing at least aluminum as a group III element, and a nitride-based III-V group compound. And a step of forming the electron transit layer, the composition ratio of aluminum is 10 to 18%, and the film thickness is 5 to 15 nm. Forming the electron supply layer while controlling the gas supply amount, and epitaxial growth in both steps is performed by MOCVD (Metal Organic Chemical Vapor Deposition) method, MBE (Molecular Beam Epitaxy). The gist is to use either the molecular beam epitaxy (HVPE) method or the HVPE (Hydride Vapor Phase Epitaxy) method.

According to the solution 3, as in the solution 1 described above, the occurrence of cracks and the like is prevented, and the manufactured semiconductor device is normally off. In addition, since both steps are performed for any of the MOCVD method, the MBE method, and the HVPE method, the substrate being manufactured is not exposed to the air to replace the apparatus. Therefore, the interface is prevented from being deteriorated and the reliability of the device is increased.
In addition to the method described above, it is also possible to perform epitaxial growth using, for example, an ALE (Atomic Layer Epitaxy) method.

  According to the present invention, the film thickness and the Al composition ratio of the electron supply layer (that is, the nitride III-V compound layer containing at least aluminum as a group III element) are optimized, and the semiconductor device is normally off. A manufacturing method can be provided.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  First, FIG. 1 is a cross-sectional view showing a configuration example of a semiconductor device according to the present invention. In the semiconductor device 10 shown in FIG. 1, an electron transit layer 17 is formed on a substrate 18 by epitaxial growth, and an electron supply layer 15 is further formed on the electron transit layer 17 by epitaxial growth. The electron transit layer 17 and the electron supply layer 15 have a heterojunction structure, and a HEMT capable of forming a two-dimensional electron gas channel 16 at the junction interface. The electron supply layer 15 is covered with an insulating film 14, and a source electrode 11, a gate electrode 12, and a drain electrode 13 are provided. The substrate 18 is made of, for example, SiC (silicon nitride). The insulating film 14 is made of, for example, AlN (aluminum nitride).

  The electron transit layer 17 is formed of a nitride III-V group compound, for example, GaN. In this example, the electron transit layer 17 is formed of a plurality of layers including an LT-GaN layer (a GaN layer grown at a low temperature) and a GaN layer.

  The electron supply layer 15 is formed of a nitride III-V group compound containing at least aluminum as a group III element, for example, AlGaN. The electron supply layer 15 is formed with an Al composition ratio of 10 to 18 [%] and a film thickness of 5 to 15 [nm].

  A method of manufacturing the semiconductor device 10 having the above-described configuration will be described with reference to FIG. FIG. 2 is a cross-sectional view schematically showing an example of the MOCVD apparatus. Specifically, a horizontal section is shown in FIG. 2A, and a vertical section is shown in FIG. The MOCVD apparatus 20 shown in FIG. 2 includes a supply port 21, a reaction unit 22, a discharge port 23, a turntable 25, a heater 26, a driving means 28, and the like. The supply port 21 is filled with a gas containing a raw material necessary for epitaxial growth. In this example, as shown in FIG. 2B, three supply ports 21a, 21b, and 21c are provided to supply three types of gases. In the example of FIG. 2B, nitrogen gas is supplied from the supply port 21a, gas containing a group III element and a carrier (for example, nitrogen gas or hydrogen gas) is supplied from the supply port 21b, and from the supply port 21c. A gas containing a group V element and a carrier is supplied.

  In the reaction unit 22, as shown in FIG. 2B, a laminar flow region and a diffusion region are provided between the supply port 21 and the turntable 25. In the laminar flow region, a partition plate 22a is provided on the supply port side in order to stabilize the gas supplied from each supply port into a laminar flow. The diffusion region is between the laminar flow region and the turntable 25, and the gas supplied from each supply port is mixed because there is no partition plate 22a.

  The upper surface of the turntable 25 is formed in a concave shape, and the wafer 24 is placed in this concave portion. The turntable 25 is fixed to the rotary shaft 27 of the drive means 28 and is rotated by performing drive control of the drive means 28. The heater 26 is provided below the turntable 25 and heats the wafer 24 through the turntable 25. The drive unit 28 includes a drive source (for example, a motor) and a control circuit. The electron transit layer 17, the electron supply layer 15, the insulating film 14, and the like are formed on the wafer 24 by epitaxial growth while controlling the type of gas, the supply speed of each gas, and the rotation speed of the turntable 25. Below, the specific example of the process of forming each layer is demonstrated easily.

(Step 1) Formation of LT-GaN Layer Corresponding to Electron Traveling Layer 17 The reaction section 22 is adjusted to a low temperature (around 700 ° C.), and TMG (trimethylgallium) gas and NH ₃ (ammonia) gas are reacted to form a substrate 18. An LT-GaN layer is formed thereon.

(Step 2) Formation of a GaN layer corresponding to the electron transit layer 17 The reaction section 22 is adjusted to a high temperature (about 1100 ° C.), and TMG gas, NH ₃ gas, and SiH ₄ (monosilane) gas as an impurity are reacted to produce LT− A GaN layer is formed on the GaN layer.

(Step 3) Formation of an AlGaN layer corresponding to the electron supply layer 15 The reaction part 22 is adjusted to a high temperature (about 1100 ° C.), and TMG gas, NH ₃ gas, and TMA (trimethylaluminum) gas are reacted to form an AlGaN layer. To do. However, in order to make the Al composition ratio 10 to 18%, the supply amount of each gas is controlled so that Al and Ga have a predetermined ratio. Further, the gas supply amount, growth time, and the like are controlled so that the film thickness becomes 5 to 15 [nm].

(Step 4) Formation of an AlN layer corresponding to the insulating film 14 The reaction part 22 is again adjusted to a low temperature (around 700 ° C.), and an AlN gas is formed by continuously supplying or intermittently supplying Al material gas and NH ₃ gas. .

  If the process up to step 4 is performed, the insulating film 14 is formed, and the source electrode 11, the gate electrode 12, and the drain electrode 13 are formed after removing the insulating film 14 and part of the electron supply layer 15. The material of these electrodes is, for example, Ti (titanium) or Au (gold), and is formed by a vapor deposition method, a lift-off method, or the like. Thereafter, when it is appropriately cut, the semiconductor device 10 of FIG. 1 is obtained.

The characteristics of the semiconductor device 10 manufactured as described above will be described with reference to FIGS. FIG. 3 is a graph showing a relationship in which the horizontal axis represents the Al composition ratio [%] and the vertical axis represents the threshold voltage V _th [V] of the gate electrode 12. FIG. 4 is a graph showing a relationship in which the horizontal axis represents the film thickness [nm] of the AlGaN layer and the vertical axis represents the threshold voltage V _th [V] of the gate electrode 12.

FIG. 3 shows the threshold voltage V _th when the semiconductor device 10 is manufactured with the AlGaN layer thickness set to 5, 10, 15, 20, 26 [nm] and the Al composition ratio changed for each thickness. . FIG. 4 shows threshold voltages V _th when the Al composition ratio is 5, 10, 15, 20, 25, 35, 45, 55 [%] and the semiconductor device 10 is manufactured with the thickness of the AlGaN layer changed. Represents. In order for the manufactured semiconductor device 10 to be normally off, the threshold voltage V _th shown in FIGS. 3 and 4 must be 0 [V] or more. As shown by hatching, the film thickness of the AlGaN layer is in the range of 5 to 15 [nm], and the Al composition ratio is in the range of 10 to 18 [%].
Since the semiconductor device of Patent Document 1 has an AlGaN layer thickness of 10 [nm] or more and an Al composition ratio of 25 [%] or more, both are normally on when applied to FIGS. It is clear that

According to the embodiment described above, the following effects can be obtained.
(1) The electron supply layer 15 was formed by epitaxial growth with an Al composition ratio of 10 to 18 [%] and a film thickness of 5 to 15 [nm] (see FIG. 1). The produced semiconductor device 10 is normally off (see FIG. 3 and FIG. 4), preventing the occurrence of cracks and the like. Therefore, this semiconductor device 10 can be used as a power device.

(2) The HEMT was formed as a two-dimensional electron gas channel 16 at the junction interface between the electron supply layer 15 and the electron transit layer 17 (see FIG. 1). Therefore, the HEMT semiconductor device 10 can be used as a power device.

(3) Steps 1 and 2 for forming the electron transit layer 17 and Step 3 for forming the electron supply layer 15 having an Al composition ratio of 10 to 18 [%] and a film thickness of 5 to 15 [nm]. Then, the epitaxial growth in steps 1 to 4 was performed using the MOCVD method. The produced semiconductor device 10 is normally off (see FIG. 3 and FIG. 4), preventing the occurrence of cracks and the like. Therefore, this semiconductor device 10 can be used as a power device.
In addition, since the steps 1 to 4 are performed by the MOCVD method (that is, performed in the same MOCVD apparatus 20), it is not necessary to expose the substrate 18 being manufactured to the air for replacing the apparatus. Therefore, the interface is prevented from being deteriorated and the reliability of the device is increased.

[Other Embodiments]
Although the best mode for carrying out the present invention has been described above, the present invention is not limited to this mode. In other words, various forms can be implemented without departing from the scope of the present invention. For example, the following forms may be realized.

(1) In the embodiment described above, AlGaN is applied to the electron supply layer 15 (see FIG. 1 and the like). Instead of this form, other nitride-based III-V group compounds may be applied although it is a condition that at least aluminum is included. That is, the group III element may include at least one of the group consisting of Ga (gallium), Al (aluminum), B (boron), and In (indium), and the group V element includes N (nitrogen), P (phosphorus). ) And As (arsenic) may be included. For example, AlGaAs (aluminum gallium arsenide), AlGaP (aluminum gallium phosphide), and the like are applicable.
Further, a compound in which indium is used instead of gallium contained in these compounds, for example, AlInN (aluminum indium nitride), AlInAs (aluminum indium arsenide), AlInP (aluminum indium phosphide), or the like may be applied.
Regardless of the compound, by setting the film thickness in the range of 5 to 15 [nm] and the Al composition ratio in the range of 10 to 18 [%], it is possible to obtain the same effects as the above-described embodiment. it can.

(2) In the above-described embodiment, GaN is applied to the electron transit layer 17 (see FIG. 1 and the like). Instead of this form, other nitride III-V compounds may be applied. Group III elements and Group V elements are the same as in (1) above. For example, GaAs (gallium arsenide), GaP (gallium phosphide), and the like are applicable. Further, a compound in which indium is applied instead of gallium contained in these compounds, for example, InN (indium nitride), InAs (indium arsenide), InP (indium phosphide), or the like may be applied. Whichever compound is used, the same effect as that of the above-described embodiment can be obtained.

  The electron transit layer 17 is formed of a plurality of layers including an LT-GaN layer and a GaN layer (see FIG. 1 and steps 1 and 2). It may replace with this form and may form with the single layer which consists only of a GaN layer. In this case, since step 1 is not necessary, it is possible to reduce labor and cost for manufacturing the semiconductor device 10.

(3) In the above-described embodiment, the substrate 18 is made of SiC, and the insulating film 14 is made of AlN (see FIG. 1 and the like). Instead of this form, the substrate 18 may be made of Al ₂ O ₃ (sapphire), Si (silicon), or the like. Similarly, the insulating film 14 is composed of any one of SiO ₂ (silicon dioxide), SiON (silicon nitride oxide), borazine-silicon polymer (a polymer having a network structure in which borazine and silicon compounds are alternately connected), and the like. Also good. Whichever compound is used, the same effect as that of the above-described embodiment can be obtained.

(4) In the above-described embodiment, the epitaxial growth was performed by the MOCVD method (see FIG. 2 and steps 1 to 4). Instead of this form, epitaxial growth may be performed by other methods. For example, the MBE method and the HVPE method are applicable. In any method, since the steps 1 to 4 are performed in the same apparatus, it is not necessary to expose the substrate 18 being manufactured to the air for replacing the apparatus. Therefore, the interface is prevented from being deteriorated and the reliability of the device is increased.

(5) In the above-described embodiment, the semiconductor device 10 is a HEMT that forms a two-dimensional electron gas at the bonding interface between the electron supply layer 15 and the electron transit layer 17 (see FIG. 1 and the like). Instead of this form, the semiconductor device 10 may be a MESFET. That is, after the electron supply layer 15 and the electron transit layer 17 are epitaxially grown on the substrate 18, the electron supply layer 15 and the like are etched to form a mesa, and a metal electrode (that is, the source electrode 11, the gate electrode 12,. A drain electrode 13) is formed and manufactured. Even when the MESFET is formed in this way, the same effects as those of the above-described embodiment can be obtained as a normally-off semiconductor device.

It is sectional drawing which represents typically the structural example of a semiconductor device. It is sectional drawing showing an example of a MOCVD apparatus typically. It is a graph showing the relationship between Al composition ratio and threshold voltage. It is a graph showing the relationship between the film thickness of an electron supply layer and a threshold voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor device 11 Source electrode 12 Gate electrode 13 Drain electrode 14 Insulating film 15 Electron supply layer 16 Two-dimensional electron gas channel 17 Electron travel layer 18 Substrate 20 MOCVD apparatus 21 (21a, 21b, 21c) Supply port 22 Reaction part 22a Partition plate 23 Discharge port 24 Wafer 25 Turntable 26 Heater 27 Rotating shaft 28 Driving means

Claims (3)

A heterojunction of an electron supply layer formed on a substrate and formed of a nitride III-V compound containing at least aluminum as a group III element and an electron transit layer formed of a nitride III-V compound A semiconductor device having a structure,
The electron supply layer is a semiconductor device formed with an aluminum composition ratio of 10 to 18% and a film thickness of 5 to 15 nm. A semiconductor device according to claim 1,
A semiconductor device that is a HEMT or MESFET that forms a two-dimensional electron gas at a junction interface between an electron supply layer and an electron transit layer. A heterojunction of an electron supply layer formed on a substrate and formed of a nitride III-V compound containing at least aluminum as a group III element and an electron transit layer formed of a nitride III-V compound A method of manufacturing a semiconductor device having a structure,
Forming the electron transit layer;
Forming the electron supply layer while controlling the gas supply amount so that the composition ratio of aluminum is 10 to 18% and the film thickness is 5 to 15 nm,
A method of manufacturing a semiconductor device, in which epitaxial growth in both steps is performed by using either MOCVD, MBE, or HVPE.

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